KLN 89B CDI Error

Joe

Joe

Well-Known Member
My flight school operates several Cessna 172Rs equipped with the Bendix-King KLN 89B, and they all seem to have the same issue: When set to GPS (instead of NAV), the #1 CDI (which is interfaced with the GPS) is off by 105°. For example, on the self-test page on startup, if you twist the OBS on the CDI to 105°, the GPS OBS will display 000°. What's even more strange is that the amount of error is the same in each aircraft, and I don't remember experiencing this when I was working on my instrument rating a few years ago. It's not too much of a problem in Leg mode, as the needle stays centered regardless of what your OBS is set to, but you will get messages telling you to adjust your nav course. It's more of a problem in OBS mode (which is the case when vectored to final for a GPS approach, doing a procedure turn, or holding after executing the missed). Anyway, as a result, you are left navigating with the CDI on the GPS display, which you lose when you go to any other page.

Has anyone ever seen this before, and does anyone know how it could be fixed?
 
Joe said:
Has anyone ever seen this before, and does anyone know how it could be fixed?
Click to expand...

Yes, it sometimes needs to be recalibrated via the setup screens for the 89B. Should be in the installation manual. I used to have the relevant pages around here somewhere...
 
This calibration is actually in the hidden maintenance pages, not the setup pages if I recall correctly. It's on maintenace page 3. There is a procedure to get to the maintenance pages when starting up. I think it is hold down MSG before start up, start up and continue holding it for a while. Here is the procedure on how to calibrate a KLN-94, and I think it is similar:

2.4.1.3 Maintenance 3 (MNT 3) Page
The MNT 3 page is used to calibrate the OBS setting of the aircraft’s HSI or CDI to the KLN 94 so
that the KLN 94 reads the value the pilot selects on the HSI or CDI. It is necessary to configure
this page only if the KLN 94 is interfaced to an HSI or CDI resolver such that the KLN 94 is able
to read the course selected on the HSI or CDI. To calibrate the OBS:
1.Select a course using the course select/OBS knob on the HSI or OBS that is interfaced with the
KLN 94. It is suggested that a course increment of 10 degrees (example 10,150, 270, etc.) be
used so that the course can be selected as precisely as possible.
2.Press the CRSR button to turn on the cursor.
3.Use the small inner knob to select the exact course that is selected on the HSI or CDI in step 1
above.
4.Adjust the HSI or CDI to another course which is not 180× away from the original course, and
verify the correct course is displayed within 2×. If not, the OBS resolver interface may be
miswired.
5.Press the CRSR button to turn off the cursor. The calibration is now complete.
Click to expand...
 
Here, this is the procedure to enter the maintenance page on a KLN-89B:

"To enter the maintenance pages, the MSG button must be depressed before the unit is turned on and continue to be depressed for 10 seconds (+/- 2 seconds) after turn on. At the end of the 10-second period, release the MSG button for 1 second and momentarily press the button again. Following this sequence, the unit will automatically enter the Maintenance (MNT) pages."
 
Awesome, that seemed to do the trick, thanks! I have no idea how they all ended up off by the same amount, but I'll see if it stays accurate.
 
Im so glad I found this thread.. I have the SAME problems at my flight school

Where are you at Joe??
 
Joe said:
Awesome, that seemed to do the trick, thanks! I have no idea how they all ended up off by the same amount, but I'll see if it stays accurate.
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Just a guess, but the initial true course from your neck of the woods to 0°N, 0°E is 102.5° (your magnetic declination ruins my theory so I chose to ignore it :D)
 
Did someone recently quit, get fired or get hired? It sounds like with them all being the same degree off, someone either made a huge mistake, or was messing with you.
 
it sounds more like they were never calibrated OR, somehow the KLN 89/94 doesn't keep any calibration info when the battery dies. Everytime the plane goes for a 100Hr the clock comes back off, so I have a feeling the calibration would come back off as well.

I'm gonna calibrate it this weekend and see what happens next time I fly it
 
elmetal said:
it sounds more like they were never calibrated OR, somehow the KLN 89/94 doesn't keep any calibration info when the battery dies. Everytime the plane goes for a 100Hr the clock comes back off, so I have a feeling the calibration would come back off as well.

I'm gonna calibrate it this weekend and see what happens next time I fly it
Click to expand...

It should write that data into memory that is not erased when it loses its battery.
 
elmetal said:
Im so glad I found this thread.. I have the SAME problems at my flight school

Where are you at Joe??
Click to expand...

elmetal said:
it sounds more like they were never calibrated OR, somehow the KLN 89/94 doesn't keep any calibration info when the battery dies. Everytime the plane goes for a 100Hr the clock comes back off, so I have a feeling the calibration would come back off as well.

I'm gonna calibrate it this weekend and see what happens next time I fly it
Click to expand...

I fly out of PVD. They had been calibrated before, because when I did my instrument training back in 2006/2007 we didn't have this problem. I was doing a GPS approach with the KLN 89B for the first time in years a few months ago and noticed it, and then began to notice it in the other planes as well. I'll keep an eye on it, especially when they come out of 100hr or annual.

mshunter said:
Did someone recently quit, get fired or get hired? It sounds like with them all being the same degree off, someone either made a huge mistake, or was messing with you.
Click to expand...

We've had a few instructors leave this year but I highly doubt anyone would do something like that... plus, we have a second location at OWD, and the planes up there have the same issue.
 
Joe said:
We've had a few instructors leave this year but I highly doubt anyone would do something like that... plus, we have a second location at OWD, and the planes up there have the same issue.
Click to expand...

Sounds like someone made a error to me. All of them off by the same amount........

Sounds like an "Oops" moment.
 
mshunter said:
Sounds like someone made a error to me. All of them off by the same amount........

Sounds like an "Oops" moment.
Click to expand...
I thought it would be the same thing but how can you mess up calibration in 2 ends of the country by the same 105 degrees?

What method could they possibly be using besides using the OBS as it should be?


I'm trying to figure out maybe they thought the pointer on the OBS should be I dont even know I cant make sense of it
 
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